Level control for hydraulic press brakes and the like



Sept. 30, 19.69 G. H. TRAU'TMAN, .IRl

i `LEVEL CONTROL FOR HYDRAULIC PRESS BRAKES AND THE LIKE Filed Aug. 8, 1966 INVENTOR. GEORGE /v /"/UTMHA/,L/R.

ATTORNEYS United States Patent C) 3,469,435 LEVEL CONTROL FR HYDRAULIC PRESS BRAKES AND THE LIKE George H. Trautman, Jr., Kenmore, N.Y., assignor to Niagara Machine & Tool Works, Buffalo, N.Y.

Filed Aug. 8, 1966, Ser. No. 571,032 Int. Cl. B215 9/14 U.S. Cl. 72-453 16 Claims ABSTRACT F THE DISCLOSURE A level control for a machine having a member of substantial width movable toward and away from an opposed member by means of a pair of hydraulic motors which act simultaneously against laterally spaced points on the movable member when supplied with operating pressure fluid through a pair of supply conduits from a pump. A valve is provided with a pair of outlet conduits to the supply conduits and an input conduit to the pump. The valve is normally blocked but shiftable to supply additional pressure iiuid from the input conduit to the supply conduit of whichever of the motors is lagging, in response to the operation of mechanical means connected to the movable member for sensing unequal movements of laterally spaced points thereon.

This invention relates to press brakes and similar cyclic metal forming presses or other reciprocating machines and more particularly to presses and the like wherein a ram or movable platen is reciprocated by hydraulic motor means.

In hydraulic press brakes and other hydraulic presses or shears wherein the area or width of the working surface of the press is of substantial extent, it is desirable and common to employ a pair of laterally spaced hydraulic piston and cylinder devices or other hydraulically energized actuators for reciprocating the ram or movable platen by hydraulic motor forces applied at such spaced points, as for instance, adjacent to the opposite ends of the ram in a press brake.

This general drive arrangement presents a problem in synchronizing the vertical movements of the opposite ends or sides of such a ram or movable platen or, stated another way, necessitates special arrangements or provisions for maintaining an accurately level attitude of the ram or movable platen during its descent and ascent. This problem is aggravated by the natural tendency of a ram or platen to go out of level under eccentric loading, the side of the ram or platen having the lesser load naturally tending to descend ahead of the heavier loaded side.

In the prior art various levelling arrangements for hy draulic machines of this type have been proposed and employed wherein level-sensing means controls a valve which, upon the occurrence of an out-of-level condition, bleeds hydraulic fluid from the leading cylinder whereby its movement is retarded until the pair of cylinders are again in synchronism. Examples of arrangements of this type are found in Castle Patent No. 2,558,071, Hazelton et al. Patent No. 2,978,976 and Munschauer et al. Patent No. 3,059,431.

While bleeding fluid from the leading cylinder has been generally adopted for automatic levelling of cylinders in the hydraulic press brake lield, this exepdient is subject to numerous practical objections and difliculties. First, there is an obvious ineiciency in draining iiuid from the hydraulic system which is unavoidable in attaining automatic leveling in this manner. Secondly, these bleeding arrangements are prone to starting diiiculties after the machine has been idle for some time. The cause of this 3,469,435 Patented Sept. 30, 1969 ice difficulty is not known but appears to result from slow drainage or siphonage of iiuid through the bleed valve, especially if the machine is stopped when not exactly level or when one side drifts slightly out of level during idle periods.

Furthermore, in this prior art system, when one side of a ram or crosshead drifts downwardly the condition is not corrected since the other side cannot drain freely due to the presence of conventional counterbalance valves in each side of the system.

The present levelling system accomplishes the desired purposes without adding or substracting fluid from the system which supplies fluid to the two cylinders. Means are provided whereby, when an out-of-level condition arises, a proportionately greater amount of the Huid supply is automatically directed to the cylinder at the lagging side. More speciiically, this is accomplished by actually adding iiuid to the conduit which supplies fluid to the cylinder at the lagging side to cause the piston of such cylinder to advance to a position of synchronism with the piston of the other cylinder.

This novel arrangement avoids many objections which accompany prior art arrangements. The above mentioned starting difliculties are avoided since the positive pressure applied by way of the level compensating valve insures a fully pressured system. Also, when the machine is idle with the pumping system running, the by-pass pressure is sufficient to maintain the ram or platen in a level raised position. Furthermore, full operating pressure is maintained since there is no impoverishment of the system due to bleeding uid therefrom.

While a single specic embodiment of the principles of the present invention is illustrated in the accompanying drawing and described in detail in the following specification, it is to be understood that such embodiment is by way of example only and that various mechanical modifications may be made without departing from the spirit of the invention the scope of which is limited only as defined in the appended claims.

The single lligure of the drawing is a schematic showing of one form of the hydraulic drive and self-leveling system of the present invention.

In the drawing, the numeral 10 designates the usual reciprocable crosshead or ram of -a press brake and the numerals 11 and 12 designate hydraulic cylinders which overlie the crosshead 10 at opposite sides thereof and are provided with pistons 13 and 14', respectively, whose lower ends engage the crosshead 10 as at 15 and 16, respectively, to reciprocate the crosshead by liuid pressure actuation of the pistons 13 and 14 in the cylinders 11 and 12.

We shall first describe the main liuid circuits from the hy-draulic pressure generating means to the cylinders. A pair of pumps 20 and 21 are driven from a common electric motor 22, the pumps having intake conduits 24 and 25, respectively, which draw fluid from a reservoir 26. The showing of the reservoir 26 is repeated at various parts of the diagram merely for simplicity of illustration, it being understood that the various reservoir indications 26 constitute in fact one common reservoir. The numerals 27 and 28 designate filter units interposed in the intake conduits 24 and 25.

The numerals 30 and 31 designate output conduits from the pumps 20 and 21, respectively, and these main conduits lead through several control and pressure regulating valves to the main directional valves, presently to be described.

The main return conduits designated 33 and 34 lead from the above-mentioned main directional valves back to the reservoir 26.

Each pair of main supply pressure and return conduits leads to a main directional valve, the main directional valve for the supply conduit 30 and return conduit 33 being designated 37 and the main directional valve for the supply conduit 31 and return conduit 34 being designated 38. The valves 37 and 38 are conventional four way pilotoperated valves.

The main directional valves 37 and 38 are mechanically interconnected for joint lineal shifting movement by a rod 40 and are actuated in opposite directions by a pilot directional valve 39 which inthe present instance is solenoidcontrolled to shift between positions for moving the crosshead successively down and up by electrical switch means such as limit switches interposed in the path of the crosshead to be actuated at opposite ends of its stroke. The connections from pilot valve 39 to the pilot operated directional valves 37 and 38 are designated 41 and 42, respectively..

The schematic drawing shows digrammatically a representative mechanism arrangement for measuring or sensing out-of-level conditions in the crosshead or ram 10 and for translating such indications or measurements into a proportionate hydraulic fluid tlow control impulse. A pair of idler pulleys 43 and 44 are fixed to the crosshead 10 -at opposite sides thereof to reciprocate vertically with the crosshead 10.

A tape or cable element 46 is adjustably anchored at one end to a bracket 47 which is Xed to the machine. Bracket 47 may include mechanism such as is shown at 47 and 48 in FIG. 1 of Munschauer et al. Patent No. 3,059,431 to establish an initial level setting of valve 52 and to provide predetermined tilt adjustment where 4desired. The other end of tape 46 is Xed to a spool valve element of a three position closed center directional valve 52.

The spool valve element of valve 52 is normally centered to close all valve passages and the manner in which it functions to correct out-of-level conditions of the press ram will presently be described.

Operating pressure for valve S2 is provided by a conduit 54 which leads from conduits S5 and 56 from the main supply conduits 30 and 31, respectively. The conduits 55 and 56 include check valves 57 and 58 which permit fluid ow to conduit 54 from either of the supply conduits 30 or 31 but prevent retrograde tlow. Fluid pressure for leveling ram 10 is supplied through either of conduits 60 and 61 from valve 52, depending upon the direction of deviation of ram 10 as sensed by tape 46. Conduits 60 and 61 lead to a reversing valve 62 which is connected to rod 40 so that valve 62 reverses with directional valves 37 and 38 and the system thus levels ram it) with equal eicacy on both the down and up strokes of ram 10. Conduits 63 and 64 from reversing valve 62 lead to pressure supply conduits 30 and 31.

In the diagram the numerals 67 and 68 designate pressure control valves interposed in pressure supply conduits 30 and 31, the operation of which in ram leveling operation will presently be described. The valves 67 and 68 are commercially known -as sequence valves which are pressure reducing valves of a particular type which reduce the pressure coming from supply conduits 30 and 31 by a predetermined amount so that the pressure at the outlet side of each valve 67 and 68 is always less than the pressure at the inlet side by a constant amount, for instance, 100 p.s.i.

The conduits from the directional valves 37 and 38 to the upper ends of cylinders 11 and 12 are designated 70 and 71, respectively, and the conduits, from the directional valves to the lower ends of cylinders 11 and 12 are designated 72 and 73, respectively. Conventinal counterbalance valves 74 and 75 are interposed in conduits 72 and 73 and are adjusted to counterbalance the weight of ram 10 and the die or other parts carried thereby.

The unit designated generally 80 in the drawing is a control unit for initiating operating cycles of the system and includes a pressure relief valve 81 and a two-way solenoid operated valve 82 having an operating solenoid 83. As shown in the diagram the system is in idle position and the output of pumps and 21 goes by way of conduits 30, 31 and 55, 56 to relief valve 81, thence directly to the reservoir 26. A drain passage 85 from valve 81 leads to a two-way valve 82 which causes valve 81 to dump -directly to reservoir 26 when valve 82 is in the position shown. Pressure relief valve 81 may be set to maintain a desired minimum pressure in conduits 30, 31 and 55, 56, say 75 p.s.i., for the purpose of supplying operating pressure for various auxiliary purposes such as for supplying pilot pressure to a conduit 86 which leads to valve 39 and thus supplies pilot operating pressure t0 directional valves 37 and 33.

When solenoid 83 is operated to initiate movement of ram 10 valve 82 shifts to block drain passage 85 and full output pressure of pumps 20 and 21 is applied to pressure reducing valves 67 and 68. In the drawing the directional Valves 37 and 38 are positioned to effect downward movement of ram 10. The valves 37 and 38 are controllable as to direction by a solenoid 88 of pilot valve 39 and solenoid 88 is arranged to be operated either manually or automatically by limit switches positioned on the machine so as to be engaged by ram 10 at desired upper and lower limits of movement, this general switch arrangement being conventional.

Levelling operation of the foregoing system will now be described in connection with downward movement of ram 10 although it is to be understood that levelling will be similarly attained during upward movement due to the shifting of reversing valve 62 which accompanies shifting of the directional valves 37 and 38. Levelling operation is controlled by valve 52 which is a servo-valve of the general type described in Munschauer et al. Patent 3,059,431, and illustrated therein at 52 in FIG. 1.

As shown in this patent, the valve spool which controls the flow of fluid from the pressure conduit 54 of valve 52 to either of the outlet conduits 60 or 61 has a lineto-line seal with the discharge passages and is so constructed that shifting movement of the valve spool in either direction establishes tluid flow of variable quantity to a conduit 60 or 61 proportionally to the degree of shifting movement of the valve spool.

However, apart from this mechanical similarity in the servo-valves as to proportional flow, the valve 52 of the present application differs fundamentally from the corresponding valve of the foregoing patent in that the valve of the patent is merely a bleed valve for discharging fluid from either side of the system to drain, whereas the valve 52 of the present application has a pressure supply conduit connection 54 which is arranged to supply a tluid pressure which is at all times in excess of the pressure obtaining in the conduits 30 and 31 between the pressure reducing valves 67 and 68 and the directional -valves 37 and 38. Check valves 93 and 94 are interposed in conduits 60 and 61 and it will be noted that the static pressure in conduits 63 and 64 and in conduits 60 and 61 between conduits 63 and 64 and the check valves will be the same as in the conduits 30 and 31, respectively.

Due to this greater pressure in conduit 54, any shifting of the spool element of valve 52 in response to movement of tape 46 in one direction or another due to out-of-level condition establishes proportional pressure ow from conduit 54 past one or the other of check valves 93 and 94, to the corresponding conduit 60 or 61 and thence through the corresponding conduit 63 or 64 to the appropriate main pressure conduit 30 or 31. Since conduits 30 and 31 are between the pressure reducing valves 67 and 68, respectively, and the associated directional valve 37 or 38, this superior uid pressure from levelling pressure conduit 54 causes fluid ow into the conduit 30 or 31, as the case may be, and thus corrects the out-of-level condition by producing a relative advancement of the position of either piston 13 or piston 14, whichever is lagging.

In addition to establishing the required reduction of pressure in conduits 30 and 31 as described previously herein, the pressure reducing valves 67 and 68 also serve to synchronize the volumetric output of the two pumps 20 and 21 to avoid a condition, usual to eccentric loading, wherein one side of the ram has less resistance and thus imposes less back pressure against one of the pumps, which pump will then normally displace more fluid. For this purpose the iluid pressure of conduit 30 is transmitted by way of conduit 63 and a pilot connection 90 as a biasing pressure to the reducing valve 68 at the other side of the system and, conversely, fluid pressure from operating conduit 31 is transmitted by way of conduit v64. and a pilot connection 91 to serve as a regulating pressure against pressure reducing valve 67.

This arrangement causes an increase in the back pressure against the pump bearing the lighter load and this corrective action is proportioned so that the back.n` pressure on the two pumps is equalized and their volumetric output is thus equalized. This corrective action is merely auxiliary to the previously described arrrangemnt for introducing supplemental corrective iluid into either of conduits 30 or 31 to correct an out-of-level condition !by advancing the lagging piston through such pressure introduction and thereby synchronize the pistons 13 and 14..

It will be noted that check valves 93 and 94A i-n the conduits 60 and 61 from servo-valve 52 prevent retrograde flow from either of the conduits 60 or 61 to the outlet ports of the servo-valve.

I claim:

1. In a hydraulic press brake, a frame and a reciprocable ram carried thereby, a pair of hydraulic piston and cylinder mechanisms acting between said frame and spaced points along said ram and operable to reciprocate the latter, a ram level control comprising means to detect advancement of one of said mechanisms beyond the other, a iluid pressure source and a conduit therefrom to each of said mechanisms, an auxiliary conduit containing additional pressure fluid, and means responsive to said detecting means upon advancement of one of said mechanisms beyond the other for supplying additional pressure uid from said auxiliary conduit to said other mechanism to restore the mechanisms to alignment with each other.

2. Apparatus according to claim 1 including pressure reducing valves in each of the conduits to said piston and cylinder mechanisms, said additional pressure fluid supply being connected with said conduits between said pressure reducing valves and said mechanisms.

3. Apparatus according to claim 2 wherein said additional pressure fluid supply is connected to receive iluid pressure from said iluid pressure source in advance of said pressure reducing valves whereby the pressure thus received is greater than the pressure in said conduits beyond said reducing valves.

4. Apparatus according to claim 1 wherein said responsive means comprises a valve having a pair of outlet passages leading to the conduits to said mechanisms, and check valves in said passages preventing fluid flow toward said valve.

5. Apparatus according to claim 2 wherein said responsive means comprises a valve having a pair of outlet passages leading to the conduits to said mechanisms, and check valves in said passages preventing fluid ow toward said valve.

6. Apparatus according to claim 3 wherein said responsive means comprises a -valve having a pair of outlet passages leading to the conduits to said mechanisms, and check valves in said passages preventing uid ilow toward said valve.

7. Apparatus according to claim 1 wherein the conduits to said mechanisms each include reversing valves and passages from said reversing valves to opposite ends of the cylinders of said mechanisms.

8. Apparatus according to claim 7 wherein said responsive means includes pressure supply passages to each of the conduits to said mechanisms, said supply passages including reversing valve means operating jointly with the reversing valves of the conduits to said piston and cylinder mechanisms.

9. Apparatus according to claim 2 wherein the conduits to said mechanisms between said reducing valves and said mechanisms include reversing valves and passages therefrom to opposite ends of the cylinders of said mechanisms.

10. Apparatus according to claim 9 wherein the responsive means includes pressure supply passages to each ot' the conduits of said mechanisms between said reducing valves and said reversing valves.

11. Apparatus according to claim 10 wherein said pressure supply passages include reversing valve means operating jointly with the reversing valves of said mechanisms.

12. In a machine having a member of substantial width movable toward and away from an opposed member, a pair of hydraulic motors adapted to act simultaneously against laterally spaced points on said movably mounted member to reciprocate the same, pump means having a pair of outlet conduits for supplying operating pressure iluid to said motor, means for sensing unequal movements of laterally spaced points on said movably mounted member, valve means having a pair of outlet passages to said pressure supply conduits and a pressure conduit from said pump means to said valve, said valve being normally blocked but shiftable to supply pressure fluid from said last mentioned conduit to either of said valve means outlet conduits in response to operation of said sensing means to thereby add operating fluid to either of said motor operating pressure supply conduits to advance the associated motor to synchronism with the other motor.

13. Apparatus according to claim 12 including pressure reducing valves in each of said pump means outlet conduits, said valve means outlet passages connecting with said pressure supply conduits at the outlet reduced pressure sides of said reducing valves.

14. Apparatus according to claim 12 wherein said valve means outlet passages contain check valves preventing iluid ow toward said valve means from said passages.

15. Apparatus according to claim 12 wherein said valve means opens proportionately to varying degrees of movement of Said sensing means to add operating fluid to either of said motor operating conduits in proportion to the degree of unequal movement as detected by said sensing means.

16. Apparatus according to claim 1 wherein said responsive means comprises a valve having a pair of outlet passages leading to the conduits of said mechanisms, said valve being arranged to deliver pressure fluid to one or the other of said outlet passages in proportion to the degree of error sensed by said detecting means.

References Cited UNITED STATES PATENTS 2,377,007 5/ 1945 Hess 100-258 2,958,199 11/ 1960 Anderson 100-46 3,059,431 1'0/ 1962 Munschauer 100-46 3,120,799 '2/ 1964 Strnad 10G-258 CHARLES W. LANHAM, Primary Examiner GENE P. CROSBY, Assistant Examiner U.S. Cl. X.R. -258 

